1. Technical Field
This invention relates to a process and apparatus for removing metal ions from wastewater. In one aspect, this invention relates to a process and apparatus for removing copper ions from wastewater from a chemical mechanical polishing (CMP) of integrated circuit microchips.
2. Background
Semiconductor microelectronic chip (microchip) manufacturing companies have developed advanced manufacturing processes to shrink electronic circuitry on a microchip to smaller dimensions. The smaller circuitry dimensions involve smaller individual minimum feature sizes or minimum line widths on a single microchip. The smaller minimum feature sizes or minimum line widths, typically at microscopic dimensions of about 0.2-0.5 micron, provide for the fitting of more computer logic onto the microchip.
An advanced new semiconductor manufacturing technology involves the use of copper in place of aluminum and tungsten to create a copper microchip circuitry on a silicon wafer. The copper has an electrical resistance lower than aluminum, thereby providing a microchip which can operate at much faster speeds. The copper is introduced to ULSI and CMOS silicon structures and is utilized as interconnect material for vias and trenches on these silicon structures.
ULSI silicon structures are Ultra Large Scale Integration integrated circuits containing more than 50,000 gates and more than 256K memory bits. CMOS silicon structures are Complimentary Metal Oxide Semiconductor integrated circuits containing N-MOS and P-MOS transistors on the same substrate.
For fully integrated multi-level integrated circuit microchips, up to 6 levels, copper now is the preferred interconnect material.
A chemical mechanical polishing (CMP) planarization of copper metal layers is used as a part of the advanced new semiconductor manufacturing technology. The chemical mechanical polishing (CMP) planarization produces a substrate working surface for the microchip. Current technology does not etch copper effectively, so the semiconductor fabrication facility tool employs a polishing step to prepare the silicon wafer surface.
Chemical mechanical polishing (CMP) of integrated circuits today involves a planarization of semiconductor microelectronic wafers. A local planarization of the microchip operates chemically and mechanically to smooth surfaces at a microscopic level up to about 10 microns (xcexcm). A global planarization of the microchip extends above about 10 microns (xcexcm) and higher. The chemical mechanical polishing planarization equipment is used to remove materials prior to a subsequent precision integrated circuit manufacturing step.
The chemical mechanical polishing (CMP) planarization process involves a polishing slurry composed of an oxidant, an abrasive, complexing agents, and other additives. The polishing slurry is used with a polishing pad to remove excess copper from the wafer. Silicon, copper, and various trace metals are removed from the silicon structure via a chemical/mechanical slurry. The chemical/mechanical slurry is introduced to the silicon wafer on a planarization table in conjunction with polishing pads. oxidizing agents and etching solutions are introduced to control the removal of material. Deionized water rinses often are employed to remove debris from the wafer. Ultrapure water (UPW) from reverse osmosis (RO) and demineralized water also can be used in the semiconductor fabrication facility tool to rinse the silicon wafer.
The chemical mechanical polishing (CMP) planarization process introduces copper into the process water, and governmental regulatory agencies are writing regulations for the discharge of wastewater from the chemical mechanical polishing (CMP) planarization process as stringently as the wastewater from an electroplating process, even though CMP planarization is not an electroplating process.
The copper ions in solution in the wastewater must be removed from the byproduct polishing slurry for acceptable wastewater disposal.
The chemical mechanical polishing planarization of the microchip produces a byproduct xe2x80x9cgrindingxe2x80x9d (polishing) slurry wastewater which contains copper ions at a level of about 1-100 mg/l. The byproduct polishing slurry wastewater from the planarization of the microchip also contains solids sized at about 0.01-1.0 xcexcm at a level of about 500-2000 mg/l (500-2000 ppm).
An oxidizer of hydrogen peroxide (H2O2) typically is used to help dissolve the copper from the microchip. Accordingly, hydrogen peroxide (H2O2) at a level of about 300 ppm and higher also can be present in the byproduct polishing slurry wastewater.
A chelating agent such as citric acid or ammonia also can be present in the byproduct polishing slurry to facilitate keeping the copper in solution.
A chemical/mechanical slurry wastewater will discharge from the chemical mechanical polishing (CMP) tool at a flow rate of approximately 10 gpm, including rinse streams. This chemical/mechanical slurry wastewater will contain dissolved copper at a concentration of about 1-100 mg/l.
Fabrication facilities operating multiple tools will typically generate a sufficient quantity of copper to be an environmental concern when discharged to the fabrication facility""s outfall. A treatment program is needed to control the discharge of copper present in the copper CMP wastewater prior to introduction to the fabrication facility""s wastewater treatment system.
A conventional wastewater treatment system at a semiconductor fabrication facility often features pH neutralization and fluoride treatment. An xe2x80x9cend-of-pipexe2x80x9d treatment system typically does not contain equipment for removal of heavy metals such as copper. An apparatus and method for providing a point source treatment for copper removal would resolve a need to install a costly end-of-pipe copper treatment system.
Considering equipment logistics as well as waste solution characteristics, a point source copper treatment unit is needed which is compact and which can satisfy the discharge requirements of a single copper CMP tool or a cluster of copper CMP tools.
Ion exchange technology is effective for concentrating and removing low levels of contaminants from large quantities of water. Ion exchange also has been employed effectively in wastewater treatment for removal of specific contaminants. For ion exchange to remove specific contaminants from wastewater economically, it is often important to utilize a selective resin or create an ionic selectivity for the specific ion that has to be removed.
Many ion exchange resin manufacturers developed selective resins during the 1980""s. These ion exchange resins received wide acceptance because of their high capacity and high selectivity over conventional cation and anion resins for certain ions.
Cation selective resins have demonstrated their ablity to remove transition metals from solutions containing complexing agents such as gluconates, citrates, tartrates, and ammonia. These selective resins are called chelating resins, whereby the ion exchange sites latch onto the transition metal. The chelating resin breaks the chemical bond between the complexing agent or a weaker chelating chemical.
The conventional cation resins have a much greater difficulty in removing specific metals from waste streams that are chelated or contain complexing agents. The conventional resins exhibit low or no capacity for removing heavy metals in the presence of complexing or chelating compounds.
The ion exchange resin is used to pull the copper ions out of solution.
Brown, U.S. Pat. No. 4,666,683; Etzel et al., U.S. Pat. No. 4,210,530; Merchant, U.S. Pat. No. 4,329,210; and Gefart, U.S. Pat. No. 5,256,187 disclose removing copper by ion exchange.
If hydrogen peroxide (H2O2) is present, the ion exchange resin will be oxidized, and the resin structure is broken down. Accordingly, hydrogen peroxide can not be present in an ion exchange unit operation because the ion exchange resin is incompatible with hydrogen.
Hayden, U.S. Pat. No. 5,464,605, discloses removing peroxides from liquids by activated carbon.
Koehler et al., U.S. Pat. No. 3,914,374, disclose removing residual copper from acid nickel solutions by activate carbon which absorbs the copper.
Asano et al., U.S. Pat. No. 3,923,741, in Example 3 pass a copper solution through a granular active carbon column. Flow resistance is measured and reported. The solution then is passed through an ion exchange resin column. (U.S. Pat. No. 3,923,74, Col. 6, lines 35-65.) 
U.S. Pat. Nos. 5,476,883, 3,923,741, and 3,941,837 teach precipitating copper ions in wastewater solutions using a carbon column and ion resin exchange beds. In U.S. Pat. No. 5,476,883, copper is removed by strongly acidic cation exchange resin. (Col. 11, lines 36-52.) Example 8 sets up a Calgon CPG coal-based activated carbon column followed by ion exchange resin. (Col. 12, lines 55-67.) Peroxide concentrations are disclosed in Table 2.
Ion exchange can be used to attach copper ions, but would not be likely to work on a byproduct polishing slurry because of the quantities of solids coming in with the byproduct polishing slurry in the form of a silica, alumina slurry.
Conventional pretreatment practice for granular activated carbon beds also principally requires the removal of contaminants such as excess amounts of suspended solids. Suspended solids, including bacteria, in amounts exceeding about 50 mg/l are required to be removed prior to operating the carbon bed.
Ion exchange resin suppliers and equipment manufacturers strongly advise that particle controls ahead of, i.e., upstream from, ion exchange bed systems are an essential aspect of an effective pretreatment system.
According to Bayer, the feed to the ion exchange resin bed should be as free as possible of suspended solids.
Particles of suspended solids bind up the ion exchange resin beds. The resin acts as a filter to retain the particles. The suspended solids accumulate and cause an increase in pressure drop across the resin bed. When this increased pressure drop occurs, the water is forced to take the path of least resistance and circumvents or flows around the resin bed. This resin circumvention is called channeling. When the process water flows down the sides of the column, a large portion of the resin is bypassed, limiting the contact between the resin and the process water, resulting in high contaminant leakage and poor bed capacity. Under extreme conditions, internal distributors and collectors can break due to the high pressure drop.
An ion exchange bed that is loaded with solids is difficult to regenerate. The regenerant solution takes the path of least resistance and channels down the sides of the column resulting in incomplete regeneration of the resin.
According to Rohm and Haas, the feed must be relatively free from suspended solids and colloidal material. The suspended solids and colloidal matter will form a mat at the surface of the bed. Pressure drop increases, channeling is encountered, and portions of the bed are by-passed. The suspended solids and colloidal matter also coat the beads and granules of the ion exchange resin, reducing the rate of diffusion of ion in and out of the exchanger particle. It is therefore important that all feeds be clarified as much as possible to remove the last traces of suspended solids or colloidal matter. Coagulation sedimentation, and filtration are the normal clarifying methods.
The byproduct polishing slurry wastewater containing copper ions from the CMP of semiconductor microelectronic chips containing copper can be passed through a microfilter to remove the solids in the form of the silica, alumina slurry. The permeate from the microfilter containing permeate copper ions then can be contacted with the ion exchange resin to attach the copper.
Further according to Rohm and Haas, pretreatment of the feed also should remove or neutralize traces of soluble constituents that may degrade or foul the exchanger, e.g., traces of oxygen, ozone, chlorine, and other oxidants.
Wastewaters from non-copper CMP processes are generally discharged to the semiconductor fabrication facility end-of-pipe where the wastewater is neutralized prior to discharge. With the advent of copper technology, these slurry wastewaters will contain copper.
Copper present in the fabrication facility outfall can pose problems. Some fabrication facilities must control the amount of suspended solids in the out fall. Accumulation in the receiving POTW""s (Publicly Owned Treatment Works) sludges result in increased cost for municipal sludge disposal and environmental concerns to eliminate copper in the municipal sludge.
Bio-toxicity problems in the municipal biological systems are caused by mass loading of copper.
Environmental discharge limits for copper result in non-compliance at the fabrication facility.
A process and apparatus are needed to remove the copper from the waste slurries near the point of generation and permit a copper-free waste to pass to discharge and neutralization in the conventional manor.
A process and apparatus are needed to remove copper ions from solution for acceptable wastewater disposal of byproduct polishing slurries containing high amounts of suspended solids and to remove the copper ions from solution containing high amounts of suspended solids efficiently and economically.
It is an object of the present invention to provide a novel process and apparatus for removing metal ions from solution.
It is an object of the present invention to provide a novel process and apparatus for removing metal ions from solutions containing high amounts of suspended solids.
It is an object of the present invention to provide a novel process and apparatus for removing copper ions from solution.
It is an object of the present invention to provide a novel process and apparatus for removing copper ions from solutions containing high amounts of suspended solids.
It is an object of the present invention to provide a novel process and apparatus for removing copper ions from solution from a byproduct polishing slurry for acceptable wastewater disposal.
Another object of the present invention is to provide a novel process and apparatus for removing copper ions from solution from a byproduct polishing slurry from the chemical mechanical polishing (CMP) of integrated circuits.
It is a further object of the present invention to provide a novel process and apparatus for removing copper ions from solutions containing high amounts of suspended solids economically and efficiently.
These and other objects and advantages of the present invention will become more apparent to those skilled in the art in view of the following detailed description and the accompanying drawings.
The process and apparatus of the present invention remove metal ions from wastewater by providing a first step carbon adsorption bed for receiving a wastewater feed containing metal ions in solution, wherein the wastewater feed contains solids sized in the range of about 0.01-1.0 xcexcm in an amount higher than about 50 mg/l, in combination with providing a second step ion exchange unit operation for receiving a carbon bed product stream from the carbon adsorption bed and for removing the metal ions from solution. The process and apparatus of the present invention remove metal ions from wastewater containing solids in an amount higher than about 100 mg/l, e.g., by way of example in an amount in the range of about 500-2000 mg/l.
A wastewater feed containing hydrogen peroxide and metal ions in solution is passed to the carbon column to reduce the concentration of the hydrogen peroxide and form a carbon bed effluent having concentration levels of hydrogen peroxide less than about 1 mg/l (1 ppm), preferably less than about 0.1 mg/l (0.1 ppm). In one aspect, the metal ions are copper ions. In one aspect, the metal ions are copper ions at a concentration level in the range of about 1-100 mg/l.
The ion exchange unit operation includes means for contacting copper ions in the carbon bed product stream with a chelating ion exchange resin to adsorb the copper ions. In one aspect, the chelating ion exchange resin includes a macroporous iminodiacetic functional group. In one embodiment, the chelating ion exchange resin includes cross-linked polyethylene resin.
The process and apparatus of the present invention operate to remove metal ions from a wastewater from a byproduct polishing slurry. In one embodiment, the process and apparatus of the present invention operate to remove metal ions, e.g., such as copper metal ions, from a wastewater from a byproduct polishing slurry from the chemical mechanical polishing (CMP) of integrated circuit microchips to attach the metal ions and form an environmentally clean water discharge product.